The invention is particularly applicable to arc welding of stainless steel by a flux cored electrode having at least about 15% chromium and it will be described with particular reference thereto; however, the invention has broader applications and may be used for coated electrodes and submerged arc welding of various high chromium steels and other chromium-bearing alloys.
When welding a high chromium-bearing alloy such as stainless steel, it is somewhat common practice to employ welding with a flux cored electrode that is used with a shielding gas such as CO.sub.2 for the electric arc welding process. The electrode includes an outer steel sheath surrounding an inner core including a flux system in granular form and, in some instances, including alloying agents and additional iron powder. The cored electrode includes chromium in an appropriate amount, generally as powder within the core of the electrode. The chromium can be an alloying agent of the steel sheath. The core material is generally divided into the fluxing system or flux and the alloying constituents. In a high chromium electrode of the type used for flux cored arc welding of stainless steel, the fluxing system or flux often includes titanium dioxide, silica which may be in the form of a silicate, calcium fluoride and various other non-metallic compounds which react in the arc of the arc welding process to create a slag that forms over the outer surface of the weld bead to protect the weld bead until it has solidified and appropriately joined to the workpiece. This slag cover helps in forming the shape of the weld metal in the weld bead created by the flux cored arc welding process as well as protecting the molten alloy material in the weld bead until it has appropriately solidified. Stainless steel and other chromium-bearing alloys produce substantial problems in slag formation, since the chromium of the steel normally produces a chromium oxide which tends to adhere the non-metallic slag onto the outer surfaces of the weld bead. Thus, the slag adheres rigidly and tenaciously to the molten alloy of the weld bead as it is solidified. Due to the differential in thermal expansion coefficients, often the slag will be placed in compression and actually explode from the weld bead during cooling of the chromium-bearing alloy forming the weld bead. If the slag explodes from the weld bead during the solidification process, it exposes the surface of the weld bead for premature oxidation. In addition, special precautions must be taken to protect against the detrimental effect of exploding hot slag created during the welding process. Another difficulty experienced when using chromium-bearing alloy for the welding process is believed also associated with the formation of chromium oxide that has the tendency to adhere the slag onto the solidifying weld bead. If the slag remains on the weld bead, it is extremely difficult to remove, thus resulting in substantial cost and time for grinding the slag from the weld bead or otherwise removing the slag from the solidified molten chromium-bearing alloy forming the weld metal of the weld bead. All of these difficulties in welding chromium-bearing alloy are well known in the arc welding art. Thus, there is and always has been a need for a particular slag system that does not result in premature and/or violent removal of the slag during the cooling process, while also allowing convenient and inexpensive slag removal after the weld bead containing the chromium-bearing alloy has solidified and cooled. Thus, there is a substantial desire for a welding system to be used in a high chromium welding electrode or with a high chromium welding wire which will produce a slag that adheres to the molten metal alloy of the weld bead as it is being solidified for surface protection, but which can be easily removed from the weld bead after the cooling.